Conventionally, there is known a camshaft equipped with plural cams relatively rotatable (for example, Patent Document 1). Specifically, at least one of the cams is supported by an outer shaft for relative rotation, and is secured to an inner shaft via a notch of the outer shaft. A secured cam is separately provided on the outer shaft. In this case, plural cams are fitted into a base pipe to form a single unit. This unit slides over an outer peripheral surface of the outer shaft.
Also, there is known an example where an intake cam secured to the inner shaft is composed of a cylindrical member slidably supported by a cam support portion as a bulging portion integrally formed on the outer shaft (for example, Patent Document 2).